New Jersey Gov. Chris Christie speaks to fellow Republicans, last week during the Republican National Committee summer meeting in Boston.

New Jersey Gov. Chris Christie signed a bill banning the practice of administering therapy to gay minors to convert them into being straight, a move by the Republican governor that surprised some of the bill’s backers.

Mr. Christie said that while he doesn’t back government encroaching on parents’ ability to make decisions for their children, research has shown that forcing young people to change their sexual orientation can pose health risks.

In particular, Mr. Christie wrote in a bill signing Monday, the American Psychological Association has found that gay conversion can trigger depression, suicidal thoughts and substance abuse.
“I believe that exposing children to these health risks without clear evidence of benefits that outweigh these serious risks is not appropriate,” Mr. Christie wrote in the one-page signing memo. “Based upon this analysis, I sign this bill into law.”

Monday was the deadline for Mr. Christie to act on the bill banning “sexual orientation change efforts,” known as conversion therapy. The bill prohibits professional counselors from administering the therapy to those under the age of 18.

New Jersey is expected to become the first state with a ban in force, according to Garden State Equality, the state’s main gay group. California passed similar legislation, but it’s being challenged legally.

The bill’s backers said they weren’t sure where Mr. Christie stood on the issue and were thrilled that he actually signed it, as opposed to taking no action and letting it pass on its own.

“It’s amazing,” said Troy Stevenson, Garden State’s executive director. “It’s always amazing to have something to protect this many young people.”

The governor’s support of the legislation was first reported by the Associated Press.

The Republican governor doesn’t support gay marriage but has backed New Jersey’s existing civil unions, a classification that provides gay couples all the state benefits of marriage without the name. Mr. Christie, a Roman Catholic, has urged lawmakers to have state residents decide on gay marriage through a referendum rather than legislation. A case heard in state court last week seeks to force New Jersey to adopt gay marriage.

The gay conversion bill passed the Democratic-controlled Legislature in June, with a 28 senators voting for it and nine against in the Senate. In the Assembly, 56 voted for the bill, 14 against and seven abstained.